Capacitive Links for Power and Data Telemetry to Implantable Biomedical Microsystems

Abstract

Wireless interfacing is undoubtedly among the foremost requirements of a biomedical microsystem, which is a necessity for it to be full implantable. Wireless interfacing usually includes both power and data telemetry to the implanted system. Interfacing to biochips wirelessly was traditionally implemented using inductive coupling, but recently capacitive links proved to be advantageous to its inductive counterpart. In this chapter, basic concept of the employment of capacitive links for wireless interfacing to biomedical implants is discussed firstly. Then, the chapter studies practicability of the implementation of capacitive links for transcutaneous interfacing to implantable devices taking into account measured electrical properties of living tissues performing as the capacitor dielectric. Proceedingly, electrical circuit models with different levels of abstraction, which have been formed according to the physical behavior of the different parts of a capacitive link, are reviewed. Moreover, these models are also studied from a designer’s viewpoint in order to provide guidelines for the design of capacitive links in real conditions. Furthermore, the concept of wireless interfacing through capacitive coupling for both power telemetry and data exchange is explained using various case studies and examples. A study on wireless interfacing through living tissues is never complete without studying biological concerns such as the extent of the energy to which the tissue is exposed. Safety concerns associated with the exposure of living tissues to RF electromagnetic fields and the resulting energy absorption and subsequently heating are then studied. Finally, the chapter is concluded with some of the exclusive advantages of capacitive links that introduce it as an interesting method for wireless interfacing to implantable biomedical microsystems.